This invention relates to handling of materials in layers, and especially in layers on pallets and other supporting surfaces. It relates to palletizing materials and subsequently depalletizing those materials, all with a minimum amount of manual lifting on the part of attending labor or machine operators. The invention relates specifically to novel tie sheets and methods for palletizing and depalletizing layers of materials. Individual elements of material being handled may be thin as a single sheet of paper, or thicker as a magazine or a book. The material being palletized/depalletized may also be conventional cartons, boxes, and the like. Particularly with reference to cartons and boxes, the individual elements are susceptible to lateral displacement relative to each other in a layer.
Apparatus for palletizing layers of material is known in the art. A conventional palletizer for boxes or cartons may use a horizontally, reciprocally movable stripper plate for carrying boxes to a position above a pallet onto which the boxes are to be loaded. The stripper plate is then withdrawn from beneath the boxes, thereby depositing them onto the pallet. Retaining means are used for preventing the boxes from moving with the stripper plate as it is withdrawn. Such retaining means commonly include a bar which abuts the side of the boxes facing the direction of stripper plate withdrawal. Structures of this general nature are disclosed in, for example, U.S. Pat. No. 3,149,732 Gagnon et al and U.S. Pat. No. 3,833,132 Alduk.
Palletizing and depalletizing apparatus are disclosed in the following United States Patents.
______________________________________ Paxton et al 2,243,919 Samler 2,656,047 Locke 2,875,907 Woodcock 2,875,908 Keyes 2,878,948 Lazott et al 2,937,482 Reed 2,940,617 Freeman 2,978,125 Magnuson 3,105,598 Gagnon 3,149,732 McWilliams 3,157,301 Jeremiah 3,166,203 Kampert 3,257,006 Bruce 3,278,048 Roth et al 3,534,892 Grasvoll 3,594,977 Larson 3,606,310 Brockmuller 3,637,093 Grasvoll 3,648,857 Carlson 3,669,282 Von Gal Jr. et al 3,682,338 Munroe 3,720,176 Alduk 3,833,132 Dawson et al 3,836,018 Golantsev 3,837,140 Ballard 3,884,368 Beal 3,946,883 Wilde et al 3,986,620 Kelley 4,030,618 Mabey et al 4,032,021 Schmitt 4,067,456 Zimmerman 4,159,058 Schmitt 4,162,016 Shorthouse 4,172,686 Schmitt 4,195,959 Pantin 4,205,934 Faltin 4,230,311 Donnelly 4,234,280 Meratti 4,255,074 Pulda 4,339,220 Cox 4,342,531 Sylvander 4,383,788 Ishida et al 4,397,246 Werkheiser 4,422,549 Werkheiser 4,439,084 Wise 4,477,067 Feldkamper 4,671,723 Liebel 4,708,247 as well as Fed. Rep. of Germany 3,107,495 Japan 54,129661 ______________________________________
In U.S. Pat. No. 4,704,060 Winski et al herein incorporated by reference, there is disclosed palletizing apparatus for palletizing stacks of loose materials such as newspapers, signatures, sheets of paper, and the like. Winski et al disclose a stripper plate and plate movement means, for depositing material onto a pallet or onto a partial load of material on a pallet. In that teaching, underlying compressible materials are compressed by the stripper plate during the process of depositing the material. Both the material being deposited and the underlying material are prevented from moving with the stripper plate, by first and second projection means projecting into recessed portions of the top and bottom surfaces of the stripper plate. The pallet load which results from loading a pallet as disclosed therein consists of a plurality of stacks extending from the underlying pallet, or a slip sheet thereon, to the upper extremity of the stack, typically the top of the pallet load. Within that environment of continuous stacks, unloading the material from the pallet is typically done by manual labor. In that process, the material is removed in a series of steps limited by the amount of material a person can manually lift at one time.
Alternatively, unloading can be done by a depalletizer wherein essentially an entire layer of the material is pushed, or swept, off the pallet at one time. The latter case of using a depalletizer is preferred in that it reduces the chance of back injury caused by excessive manual labor at the point of depalletizing, along with the associated savings in labor costs.
However, conventional palletizers do not have the capability to stack loose materials such as newspaper and the like, except as disclosed in above-mentioned U.S. Pat. No. 4,704,060, Winski et al. And to the extent newspapers are stacked on a pallet as in Winski et al, there is not any conventionally known means for removing all of the load with known pallet unloading apparatus.
A problem with depalletizing can arise where it is desirable to remove a series of layers in sequence by pushing them off the load and wherein it is undesirable to physically restrain the intervening underlying inter-layer sheet (tie sheet, separator sheet, or spacing sheet) during layer removal by mechanical means such as clamping or . abutment.
It is an object of this invention to provide novel spacing sheets, disposed with respective layers of material, and methods of handling layers of material on a pallet with the spacing sheets. In the methods, a plurality of layers can be placed on a pallet by a palletizer, with the novel spacing sheets on top of the respective layers. The novel spacing sheet has low affinity for the respective overlying layer, and higher affinity for the respective underlying layer, such that the overlying layer can be slid off the respective spacing sheet while the spacing sheet remains stationary with respect to the underlying layer in accordance with its affinity for the underlying layer.